WO2021124970A1 - Positive electrode for nonaqueous electrolyte secondary batteries and nonaqueous electrolyte secondary battery - Google Patents

Positive electrode for nonaqueous electrolyte secondary batteries and nonaqueous electrolyte secondary battery Download PDF

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WO2021124970A1
WO2021124970A1 PCT/JP2020/045579 JP2020045579W WO2021124970A1 WO 2021124970 A1 WO2021124970 A1 WO 2021124970A1 JP 2020045579 W JP2020045579 W JP 2020045579W WO 2021124970 A1 WO2021124970 A1 WO 2021124970A1
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positive electrode
mixture layer
electrode mixture
negative electrode
electrolyte secondary
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PCT/JP2020/045579
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French (fr)
Japanese (ja)
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幸俊 上原
堂上　和範
晋也 宮崎
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三洋電機株式会社
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Priority to CN202080087516.8A priority Critical patent/CN114868276A/en
Priority to JP2021565489A priority patent/JPWO2021124970A1/ja
Priority to US17/785,211 priority patent/US20220393177A1/en
Publication of WO2021124970A1 publication Critical patent/WO2021124970A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present disclosure relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.
  • Patent Document 1 the volume ratio of the positive electrode active material to the positive electrode mixture is 97.1% to 99.6%, and the volume ratio of the voids in the positive electrode mixture layer is 16% to 22%.
  • Patent Document 2 contains polyvinylidene fluoride having a molecular weight of 600,000 to 1,000,000 as a binder, and by controlling the preparation temperature to 30 ° C. to 60 ° C., it is suitable for producing a high-capacity positive electrode mixture layer. It is disclosed that a positive electrode mixture slurry having properties can be obtained.
  • Patent Document 1 When the density of the positive electrode mixture layer is increased as disclosed in Patent Document 1, it becomes difficult for lithium ions to move between the particles of the positive electrode active material, which may result in high resistance. Further, even if polyvinylidene fluoride having a molecular weight of 600,000 to 1,000,000 is used as disclosed in Patent Document 2, if the content of polyvinylidene fluoride is small, the stability of the positive electrode mixture slurry deteriorates and the resistance is high. It may become. The techniques disclosed in Patent Documents 1 and 2 do not consider battery resistance, and there is still room for improvement.
  • the positive electrode for a non-aqueous electrolyte secondary battery which is one aspect of the present disclosure, includes a positive electrode core body and a positive electrode mixture layer formed on the surface of the positive electrode core body.
  • the void ratio of the positive electrode mixture layer is 23% by volume to 50% by volume, and the positive electrode mixture layer contains at least a positive electrode active material, carbon nanotubes as a conductive auxiliary material, and polyvinylidene fluoride as a binder.
  • the carbon nanotubes have a particle size of 5 nm to 40 nm, an aspect ratio of 100 to 1000, a content in the positive electrode mixture layer of 0.2% by mass to 5% by mass, and per unit mass of the positive electrode mixture layer.
  • the molecular quantity of polyvinylidene fluoride contained in the above is 0.005 to 0.030.
  • the non-aqueous electrolyte secondary battery includes the above-mentioned positive electrode for non-aqueous electrolyte secondary battery, negative electrode, and non-aqueous electrolyte.
  • FIG. 1 is a perspective view of a secondary battery which is an example of an embodiment, and is a diagram showing an internal structure of a battery case with the front side of the exterior body removed.
  • the dispersibility of the positive electrode active material, polyvinylidene fluoride, and carbon nanotubes in the positive electrode mixture slurry is improved, so that uniform coating is possible.
  • polyvinylidene fluoride and carbon nanotubes act in a complex manner to improve the adhesion strength between the positive electrode active materials and improve the electron conductivity. Due to these synergistic effects, the positive electrode and the battery can have low resistance. This effect can be obtained by setting the molecular quantity of polyvinylidene fluoride contained per unit mass of the positive electrode mixture layer within a predetermined range even when the amount of polyvinylidene fluoride is small.
  • the secondary battery 100 provided with the square metal exterior body 1 is illustrated, but the exterior body is not limited to the square shape, and may be, for example, a cylindrical shape or the like.
  • a winding type electrode body 3 in which a positive electrode and a negative electrode are wound via a separator is illustrated, a stack in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated one by one via a separator. It may be a type electrode body.
  • the electrode body 3 is preferably of a winding type.
  • each mixture layer is formed on both sides of each core body is illustrated, but the case where each mixture layer is formed on both sides of each core body is not limited to the case where each mixture layer is formed on both sides of each core body. It may be formed on at least one surface.
  • the secondary battery 100 includes a wound electrode body 3 in which a positive electrode and a negative electrode are wound via a separator and formed into a flat shape having a flat portion and a pair of curved portions. It includes an electrolyte, an electrode body 3, and an exterior body 1 that houses the electrolyte. Both the exterior body 1 and the sealing plate 2 are made of metal, and are preferably made of aluminum or an aluminum alloy.
  • the exterior body 1 has a bottom portion having a substantially rectangular shape when viewed from the bottom surface, and a side wall portion erected on the peripheral edge of the bottom portion.
  • the side wall is formed perpendicular to the bottom.
  • the dimensions of the exterior body 1 are not particularly limited, but as an example, the exterior body 1 has a lateral length of 60 to 160 mm, a height of 60 to 100 mm, and a thickness of 10 to 40 mm.
  • the positive electrode is a long body having a metal positive electrode core body and positive electrode mixture layers formed on both sides of the core body, and is a positive electrode core body along the longitudinal direction at one end in the lateral direction.
  • the strip-shaped positive electrode core body exposed portion 4 is formed.
  • the negative electrode is a long body having a negative electrode core made of metal and a negative electrode mixture layer formed on both sides of the core, along the longitudinal direction at one end in the lateral direction.
  • a band-shaped negative electrode core body exposed portion 5 is formed in which the negative electrode core body is exposed.
  • the positive electrode core body exposed portion 4 of the positive electrode is arranged on one end side in the axial direction
  • the negative electrode core body exposed portion 5 of the negative electrode is arranged on the other end side in the axial direction. It has a wound structure.
  • the positive electrode current collector 6 is connected to the laminated portion of the positive electrode core body exposed portion 4 of the positive electrode, and the negative electrode current collector 8 is connected to the laminated portion of the negative electrode core body exposed portion 5 of the negative electrode.
  • a suitable positive electrode current collector 6 is made of aluminum or an aluminum alloy.
  • a suitable negative electrode current collector 8 is made of copper or a copper alloy.
  • the positive electrode terminal 7 is inserted into a positive electrode external conductive portion 13 arranged on the outer side of the battery of the sealing plate 2, a positive electrode bolt portion 14 connected to the positive electrode external conductive portion 13, and a through hole provided in the sealing plate 2. It has a positive electrode insertion portion 15 and is electrically connected to the positive electrode current collector 6.
  • the negative electrode terminal 9 is provided in a negative electrode external conductive portion 16 arranged on the outer side of the battery of the sealing plate 2, a negative electrode bolt portion 17 connected to the negative electrode external conductive portion 16, and a through hole provided in the sealing plate 2. It has a negative electrode insertion portion 18 to be inserted, and is electrically connected to the negative electrode current collector 8.
  • the positive electrode terminal 7 and the positive electrode current collector 6 are fixed to the sealing plate 2 via the inner side insulating member and the outer side insulating member, respectively.
  • the internal insulating member is arranged between the sealing plate 2 and the positive electrode current collector 6, and the external insulating member is arranged between the sealing plate 2 and the positive electrode terminal 7.
  • the negative electrode terminal 9 and the negative electrode current collector 8 are fixed to the sealing plate 2 via the internal insulating member and the external insulating member, respectively.
  • the internal insulating member is arranged between the sealing plate 2 and the negative electrode current collector 8, and the external insulating member is arranged between the sealing plate 2 and the negative electrode terminal 9.
  • the electrode body 3 is housed in the exterior body 1.
  • the sealing plate 2 is connected to the opening edge of the exterior body 1 by laser welding or the like.
  • the sealing plate 2 has an electrolyte injection hole 10, and the electrolyte injection hole 10 is sealed with a sealing plug after the electrolyte is injected into the exterior body 1.
  • the sealing plate 2 is formed with a gas discharge valve 11 for discharging gas when the pressure inside the battery exceeds a predetermined value.
  • the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte constituting the electrode body 3 will be described in detail, and in particular, the positive electrode mixture layer constituting the positive electrode will be described in detail.
  • the positive electrode includes a positive electrode core body and a positive electrode mixture layer formed on the surface of the positive electrode core body.
  • a foil of a metal stable in the potential range of the positive electrode such as aluminum or an aluminum alloy, a film in which the metal is arranged on the surface layer, or the like can be used.
  • the positive electrode mixture layer contains at least a positive electrode active material, carbon nanotubes as a conductive auxiliary material (hereinafter, may be referred to as CNT), and polyvinylidene fluoride as a binder (hereinafter, may be referred to as PVdF).
  • CNT carbon nanotubes
  • PVdF polyvinylidene fluoride as a binder
  • a positive electrode mixture slurry containing a positive electrode active material, a conductive auxiliary material, a binder, etc. is applied onto the positive electrode core, the coating film is dried, and then compressed to form the positive electrode mixture layer into the positive electrode core. It can be produced by forming on both sides of.
  • the thickness of the positive electrode mixture layer is, for example, 10 ⁇ m to 150 ⁇ m on one side of the positive electrode core body.
  • the porosity of the positive electrode mixture layer is 23% by volume to 50% by volume.
  • the void ratio of the positive electrode mixture layer is as follows based on the bulk density of the positive electrode mixture layer and the true density and content of each component such as the positive electrode active material, the conductive auxiliary material, and the binder contained in the positive electrode mixture layer. It is calculated according to the formula of.
  • Porosity of the positive electrode mixture layer 1- (total of (content / true density) for each component x bulk density of the positive electrode mixture layer)
  • Examples of the positive electrode active material contained in the positive electrode mixture layer include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni.
  • Lithium transition metal oxides for example, Li x CoO 2, Li x NiO 2, Li x MnO 2, Li x Co y Ni 1-y O 2, Li x Co y M 1-y O z, Li x Ni 1- y M y O z, Li x Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F (M; Na, Mg, Sc, Y, Mn, Fe, Co, Ni , Cu, Zn, Al, Cr, Pb, Sb, B, 0 ⁇ x ⁇ 1.2, 0 ⁇ y ⁇ 0.9, 2.0 ⁇ z ⁇ 2.3). These may be used alone or in admixture of a plurality of types.
  • the positive electrode active material Li x NiO 2, Li x Co y Ni 1-y O 2, Li x Ni 1-y M y O z ( M; At least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0 ⁇ x ⁇ 1.2, 0 ⁇ y ⁇ 0. It is preferable to contain a lithium nickel composite oxide such as 9.9, 2.0 ⁇ z ⁇ 2.3).
  • the CNT contained in the positive electrode mixture layer may be either a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT).
  • MWCNTs for example, a CNT having a tubular structure in which a graphene sheet made of a 6-membered carbon ring is wound parallel to the fiber axis, and a graphene sheet made of a 6-membered carbon ring are arranged perpendicular to the fiber axis.
  • a CNT having a puretlet structure, a CNT having a herringbone structure in which a graphene sheet composed of a six-membered carbon ring is wound at an oblique angle with respect to the fiber axis, or the like can be used.
  • the positive electrode mixture layer may contain a carbon material such as carbon black, acetylene black (AB), Ketjen black, and graphite as a conductive auxiliary material.
  • the CNT has a particle size of 5 nm to 40 nm and an aspect ratio of 100 to 1000. By satisfying this range, interaction with PVdF occurs, and the positive electrode and the battery can have low resistance.
  • the particle size of CNTs is calculated from the average value of 10 CNTs measured by measuring the diameters of 10 CNTs using a scanning electron microscope (hereinafter, may be referred to as SEM).
  • the length of CNTs is calculated by measuring the lengths of 10 CNTs using SEM and averaging them. For example, the CNT is observed at an acceleration voltage of 5 kV using SEM, and the diameter and length of any 10 CNTs are measured in an image (number of pixels 1024 x 1280) of 50,000 times, and the average value thereof is measured.
  • the particle size and length can be obtained from.
  • the aspect ratio is a value obtained by dividing the length by the particle size.
  • the content of CNT in the positive electrode mixture layer is 0.2% by mass to 5% by mass, preferably 1.5% by mass to 3% by mass. Within this range, the dispersibility of CNTs in the positive electrode mixture slurry is improved, so that a positive electrode and a battery having lower resistance can be obtained.
  • the molecular quantity of PVdF contained in the unit mass of the positive electrode mixture layer is 0.005 to 0.030, preferably 0.007 to 0.011. By satisfying this range, interaction with CNT occurs, and the positive electrode and the battery can have low resistance.
  • the molecular quantity of PVdF contained in the unit mass of the positive electrode mixture layer is a value obtained by dividing the content (mass%) of PVdF in the positive electrode mixture layer by the molecular weight (g / mol) of PVdF.
  • the content of polyvinylidene fluoride in the positive electrode mixture layer may be 0.3% by mass to 2.5% by mass. As a result, a positive electrode and a battery having a lower resistance can be obtained.
  • the molecular weight of polyvinylidene fluoride may be 1.1 million to 1.4 million.
  • the positive electrode mixture layer may contain a fluororesin such as polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, etc. as a binder, and these resins may be contained.
  • PTFE polytetrafluoroethylene
  • PAN polyacrylonitrile
  • polyimide polyimide
  • acrylic resin polyolefin, etc.
  • acrylic resin polyolefin, etc.
  • CMC carboxymethyl cellulose
  • PEO polyethylene oxide
  • the negative electrode has a negative electrode core body and a negative electrode mixture layer formed on the surface of the negative electrode core body.
  • a metal foil stable in the potential range of the negative electrode such as copper or a copper alloy, a film in which the metal is arranged on the surface layer, or the like can be used.
  • the negative electrode mixture layer contains a negative electrode active material and a binder.
  • the thickness of the negative electrode mixture layer is, for example, 10 ⁇ m to 150 ⁇ m on one side of the current collector.
  • a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. is applied onto the negative electrode core body, the coating film is dried, and then rolled to form negative electrode mixture layers on both sides of the negative electrode core body. Can be produced by.
  • the negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium ions, and a carbon material such as graphite is generally used.
  • the graphite may be any of natural graphite such as scaly graphite, massive graphite and earthy graphite, and artificial graphite such as massive artificial graphite and graphitized mesophase carbon microbeads.
  • a metal alloying with Li such as Si and Sn, a metal compound containing Si and Sn and the like, a lithium titanium composite oxide and the like may be used.
  • Si-containing compounds represented by SiO x (0.5 ⁇ x ⁇ 1.6) or lithium silicate phases represented by Li 2y SiO (2 + y) (0 ⁇ y ⁇ 2) contain fine particles of Si. Dispersed Si-containing compounds and the like may be used in combination with graphite.
  • a fluororesin such as PTFE or PVdF, PAN, polyimide, acrylic resin, polyolefin or the like may be used as in the case of the positive electrode, but styrene-butadiene is preferable. Rubber (SBR) is used.
  • the negative electrode mixture layer may contain CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA) and the like.
  • the negative electrode mixture layer contains, for example, SBR and CMC or a salt thereof.
  • the separator a porous sheet having ion permeability and insulating property is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a non-woven fabric.
  • the material of the separator polyolefins such as polyethylene and polypropylene, cellulose and the like are suitable.
  • the separator may have a single-layer structure or a laminated structure. Further, the surface of the separator may be provided with a resin layer having high heat resistance such as an aramid resin and a filler layer containing a filler of an inorganic compound.
  • the non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.
  • the non-aqueous solvent for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these can be used.
  • the non-aqueous solvent may contain a halogen substituent in which at least a part of hydrogen in these solvents is substituted with a halogen atom such as fluorine.
  • halogen substituent examples include a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC), a fluorinated chain carbonate, and a fluorinated chain carboxylic acid ester such as methyl fluoropropionate (FMP).
  • FEC fluoroethylene carbonate
  • FMP fluorinated chain carboxylic acid ester
  • esters examples include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and methylpropyl carbonate.
  • Ethylpropyl carbonate chain carbonate such as methyl isopropyl carbonate
  • cyclic carboxylic acid ester such as ⁇ -butyrolactone (GBL), ⁇ -valerolactone (GVL), methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP) ), Chain carboxylic acid ester such as ethyl propionate and the like.
  • ethers examples include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahexyl, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4.
  • -Cyclic ethers such as dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether , Dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxy toluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxy Chain ethers such as ethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl
  • the electrolyte salt is preferably a lithium salt.
  • the lithium salt LiBF 4, LiClO 4, LiPF 6, LiAsF 6, LiSbF 6, LiAlCl 4, LiSCN, LiCF 3 SO 3, LiCF 3 CO 2, Li (P (C 2 O 4) F 4), LiPF 6-x (C n F 2n + 1 ) x (1 ⁇ x ⁇ 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, Li 2 B 4 O 7 , borates such as Li (B (C 2 O 4 ) F 2 ), LiN (SO 2 CF 3 ) 2 , LiN (C 1 F 2l + 1 SO 2 ) (C m F 2m + 1 SO 2 ) ⁇ l , M is an integer of 0 or more ⁇ and other imide salts.
  • lithium salt these may be used individually by 1 type, or a plurality of types may be mixed and used. Of these, LiPF 6 is preferably used from the viewpoint of ionic conductivity, electrochemical stability, and the like.
  • concentration of the lithium salt is, for example, 0.8 mol to 1.8 mol per 1 L of the non-aqueous solvent.
  • Example 1 [Preparation of positive electrode]
  • a lithium transition metal oxide represented by LiNi 1/3 Co 1/3 Mn 1/3 O 2 was used.
  • the CNT As the conductive auxiliary material, one having a particle size of 10 nm and an aspect ratio of 100 to 1000 (hereinafter referred to as CNT-A) was used.
  • CNT-A As the CNT-A was used.
  • PVdF one having a molecular weight of 1.1 million was used.
  • the positive electrode active material, CNT, and PVdF are mixed at a mass ratio of 97.3: 0.2: 2.5 and kneaded while adding N-methyl-2-pyrrolidone (NMP) to combine the positive electrodes.
  • NMP N-methyl-2-pyrrolidone
  • the positive electrode mixture slurry was applied to both sides, leaving a portion to which the positive electrode core lead made of aluminum foil was connected, and the coating film was dried. Then, the coating film was rolled using a roller so that the porosity of the positive electrode mixture layer was 50% by volume, and then cut into a predetermined electrode size to form positive electrode mixture layers on both sides of the positive electrode core.
  • a positive electrode was prepared.
  • Graphite as a negative electrode active material, sodium salt of CMC, and dispersion of SBR are mixed at a solid content mass ratio of 99 / 0.6 / 0.4, and an appropriate amount of water is added to prepare a negative electrode mixture slurry.
  • the negative electrode mixture slurry was applied and the coating film was dried, leaving the portions where the leads were connected to both sides of the negative electrode core made of copper foil.
  • the coating film was cut to a predetermined electrode size to prepare a negative electrode having negative electrode mixture layers formed on both sides of the negative electrode core.
  • the packing density of the negative electrode mixture layer was 1.17 g / cm 3 .
  • VC vinylene carbonate
  • DMC dimethyl carbonate
  • EMC ethylmethyl carbonate
  • Electrodes were attached to the negative electrode and the positive electrode, respectively, and a laminated electrode body was prepared in which each electrode was alternately laminated one by one via a separator. A single-layer polypropylene separator was used as the separator. The prepared electrode body and the non-aqueous electrolyte were housed in a square battery case to prepare a test cell.
  • Examples 2 to 14 Comparative Examples 1 to 21> Examples are shown in Tables 1 and 2, except that the content of the positive electrode active material, the type and content of the conductive auxiliary agent, the content and molecular weight of PVdF, and the porosity of the positive electrode mixture layer are changed. A positive electrode and a test cell were prepared and evaluated in the same manner as in 1.
  • the conductive auxiliary material CNT-B is a CNT having a particle size of 150 nm and an aspect ratio of 10 to 70.
  • Tables 1 and 2 summarize the results of the mixture layer resistance increase, the interface resistance increase, and the DC resistance of Examples and Comparative Examples.
  • Tables 1 and 2 also show the composition of the positive electrode mixture layer composed of the positive electrode active material, the conductive auxiliary material, and PVdF, and the porosity of the positive electrode mixture layer.

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Abstract

A positive electrode for nonaqueous electrolyte secondary batteries according to the present invention is provided with a positive electrode core body and a positive electrode mixture layer that is formed on the surface of the positive electrode core body. The positive electrode mixture layer has a void fraction of from 23% by volume to 50% by volume; the positive electrode mixture layer contains at least a positive electrode active material, carbon nanotubes serving as a conductive assistant, and a polyvinylidene fluoride serving as a binder; the carbon nanotubes have a particle diameter of from 5 nm to 40 nm and an aspect ratio of from 100 to 1,000; the content of the carbon nanotubes in the positive electrode mixture layer is from 0.2% by mass to 5% by mass; and the number of polyvinylidene fluoride molecules contained per unit mass of the positive electrode mixture layer is from 0.005 to 0.030.

Description

非水電解質二次電池用正極及び非水電解質二次電池Positive electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery
　本開示は、非水電解質二次電池用正極及び非水電解質二次電池に関する。 The present disclosure relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.
　近年、二次電池は、益々の高容量化が求められている。特許文献１には、正極合材に占める正極活物質の体積比率を９７．１％～９９．６％とし、かつ正極合材層の空隙の体積比率を１６％～２２％とすることで、正極合材層の正極活物質密度を３．７ｇ／ｃｃ以上に高密度化した高容量の二次電池が開示されている。 In recent years, secondary batteries have been required to have higher capacities. In Patent Document 1, the volume ratio of the positive electrode active material to the positive electrode mixture is 97.1% to 99.6%, and the volume ratio of the voids in the positive electrode mixture layer is 16% to 22%. A high-capacity secondary battery in which the density of the positive electrode active material of the positive electrode mixture layer is increased to 3.7 g / cc or more is disclosed.
　また、正極合材層において、結着材の含有量を少なくしつつ正極活物質の含有量を多くすることで、高容量の二次電池が得られる。特許文献２には、分子量が６０万～１００万のポリフッ化ビニリデンを結着材として含み、調製温度を３０℃～６０℃に制御することで、高容量の正極合材層の作製に好適な性状の正極合材スラリーを得られることが開示されている。 Further, in the positive electrode mixture layer, a high-capacity secondary battery can be obtained by increasing the content of the positive electrode active material while reducing the content of the binder. Patent Document 2 contains polyvinylidene fluoride having a molecular weight of 600,000 to 1,000,000 as a binder, and by controlling the preparation temperature to 30 ° C. to 60 ° C., it is suitable for producing a high-capacity positive electrode mixture layer. It is disclosed that a positive electrode mixture slurry having properties can be obtained.
特開２０１５－４３２５７号公報JP-A-2015-43257 特許第４２６３５０１号公報Japanese Patent No. 4263501
　特許文献１に開示されたように正極合材層を高密度化すると、リチウムイオンが正極活物質の粒子間を移動しづらくなり、高抵抗になってしまう場合がある。また、特許文献２に開示されたように６０万～１００万の分子量のポリフッ化ビニリデンを用いたとしても、ポリフッ化ビニリデンの含有量が少ないと正極合材スラリーの安定性が悪化し、高抵抗になってしまう場合がある。特許文献１，２に開示された技術は、電池抵抗については考慮されておらず、未だ改善の余地がある。 When the density of the positive electrode mixture layer is increased as disclosed in Patent Document 1, it becomes difficult for lithium ions to move between the particles of the positive electrode active material, which may result in high resistance. Further, even if polyvinylidene fluoride having a molecular weight of 600,000 to 1,000,000 is used as disclosed in Patent Document 2, if the content of polyvinylidene fluoride is small, the stability of the positive electrode mixture slurry deteriorates and the resistance is high. It may become. The techniques disclosed in Patent Documents 1 and 2 do not consider battery resistance, and there is still room for improvement.
　本開示の一態様である非水電解質二次電池用正極は、正極芯体と、正極芯体の表面に形成された正極合材層と、を備える。正極合材層の空隙率は、２３体積％～５０体積％であり、正極合材層は、少なくとも、正極活物質と、導電助材としてのカーボンナノチューブと、結着材としてのポリフッ化ビニリデンを含み、カーボンナノチューブは、粒子径が５ｎｍ～４０ｎｍで、アスペクト比が１００～１０００で、正極合材層における含有量が０．２質量％～５質量％であり、正極合材層の単位質量当たりに含まれるポリフッ化ビニリデンの分子数量が０．００５～０．０３０である。 The positive electrode for a non-aqueous electrolyte secondary battery, which is one aspect of the present disclosure, includes a positive electrode core body and a positive electrode mixture layer formed on the surface of the positive electrode core body. The void ratio of the positive electrode mixture layer is 23% by volume to 50% by volume, and the positive electrode mixture layer contains at least a positive electrode active material, carbon nanotubes as a conductive auxiliary material, and polyvinylidene fluoride as a binder. The carbon nanotubes have a particle size of 5 nm to 40 nm, an aspect ratio of 100 to 1000, a content in the positive electrode mixture layer of 0.2% by mass to 5% by mass, and per unit mass of the positive electrode mixture layer. The molecular quantity of polyvinylidene fluoride contained in the above is 0.005 to 0.030.
　本開示の一態様である非水電解質二次電池は、上記の非水電解質二次電池用正極と、負極と、非水電解質とを備える。 The non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes the above-mentioned positive electrode for non-aqueous electrolyte secondary battery, negative electrode, and non-aqueous electrolyte.
　本開示によれば、高容量で低抵抗の二次電池を提供することができる。 According to the present disclosure, it is possible to provide a secondary battery having a high capacity and a low resistance.
図１は、実施形態の一例である二次電池の斜視図であって、外装体の手前側を外した状態での電池ケースの内部の構造を示す図である。FIG. 1 is a perspective view of a secondary battery which is an example of an embodiment, and is a diagram showing an internal structure of a battery case with the front side of the exterior body removed.
　高容量で高出力な二次電池が求められている。空隙率を小さくして、正極合材層を高密度化することで、二次電池の高容量化を図ることができるが、リチウムイオンが正極活物質の粒子間を移動しづらくなり、二次電池が高抵抗になってしまう場合がある。本発明者らが鋭意検討した結果、正極合材層の空隙率を適切な範囲に調整しつつ、アスペクト比の高いカーボンナノチューブを所定量添加し、正極合材層の単位質量当たりに含まれるポリフッ化ビニリデンの分子数量を所定の範囲にすることで、高容量と低抵抗を両立した二次電池が得られることを見出した。ポリフッ化ビニリデンとカーボンナノチューブとの相乗効果により、正極合材スラリー中の正極活物質、ポリフッ化ビニリデン、及びカーボンナノチューブの分散性が向上したことで均一な塗布が可能となる。また、ポリフッ化ビニリデンとカーボンナノチューブが複合的に作用し、正極活物質間の密着強度を向上させ、電子伝導性が向上する。これらの相乗効果により、正極及び電池を低抵抗にすることができる。この効果は、ポリフッ化ビニリデンが少量の場合でも、正極合材層の単位質量当たりに含まれるポリフッ化ビニリデンの分子数量を所定の範囲にすることで得られる。 There is a demand for secondary batteries with high capacity and high output. By reducing the void ratio and increasing the density of the positive electrode mixture layer, it is possible to increase the capacity of the secondary battery, but it becomes difficult for lithium ions to move between the particles of the positive electrode active material, and the secondary battery becomes secondary. The battery may have high resistance. As a result of diligent studies by the present inventors, while adjusting the void ratio of the positive electrode mixture layer to an appropriate range, a predetermined amount of carbon nanotubes having a high aspect ratio is added, and the polyfoot contained per unit mass of the positive electrode mixture layer is added. It has been found that a secondary battery having both high capacity and low resistance can be obtained by setting the molecular quantity of vinylidene compound in a predetermined range. Due to the synergistic effect of polyvinylidene fluoride and carbon nanotubes, the dispersibility of the positive electrode active material, polyvinylidene fluoride, and carbon nanotubes in the positive electrode mixture slurry is improved, so that uniform coating is possible. In addition, polyvinylidene fluoride and carbon nanotubes act in a complex manner to improve the adhesion strength between the positive electrode active materials and improve the electron conductivity. Due to these synergistic effects, the positive electrode and the battery can have low resistance. This effect can be obtained by setting the molecular quantity of polyvinylidene fluoride contained per unit mass of the positive electrode mixture layer within a predetermined range even when the amount of polyvinylidene fluoride is small.
　以下、本開示の実施形態の一例について詳細に説明する。本実施形態では、角形の金属製の外装体１を備えた二次電池１００を例示するが、外装体は角形に限定されず、例えば、円筒形等であってもよい。また、正極と負極とがセパレータを介して巻回された巻回型の電極体３を例示するが、複数の正極と複数の負極とがセパレータを介して交互に１枚ずつ積層されてなる積層型の電極体であってもよい。電極体３は、巻回型であることが好ましい。また、正極及び負極の両方において、各合材層が各芯体の両面に形成される場合を例示するが、各合材層は、各芯体の両面に形成される場合に限定されず、少なくとも一方の表面に形成されればよい。 Hereinafter, an example of the embodiment of the present disclosure will be described in detail. In the present embodiment, the secondary battery 100 provided with the square metal exterior body 1 is illustrated, but the exterior body is not limited to the square shape, and may be, for example, a cylindrical shape or the like. Further, although a winding type electrode body 3 in which a positive electrode and a negative electrode are wound via a separator is illustrated, a stack in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated one by one via a separator. It may be a type electrode body. The electrode body 3 is preferably of a winding type. Further, in both the positive electrode and the negative electrode, the case where each mixture layer is formed on both sides of each core body is illustrated, but the case where each mixture layer is formed on both sides of each core body is not limited to the case where each mixture layer is formed on both sides of each core body. It may be formed on at least one surface.
　図１に例示するように、二次電池１００は、正極と負極がセパレータを介して巻回され、平坦部及び一対の湾曲部を有する扁平状に成形された巻回型の電極体３と、電解質と、電極体３及び電解質を収容する外装体１とを備える。外装体１及び封口板２はいずれも金属製であり、アルミニウム製又はアルミニウム合金製であることが好ましい。 As illustrated in FIG. 1, the secondary battery 100 includes a wound electrode body 3 in which a positive electrode and a negative electrode are wound via a separator and formed into a flat shape having a flat portion and a pair of curved portions. It includes an electrolyte, an electrode body 3, and an exterior body 1 that houses the electrolyte. Both the exterior body 1 and the sealing plate 2 are made of metal, and are preferably made of aluminum or an aluminum alloy.
　外装体１は、底面視略長方形状の底部、及び底部の周縁に立設した側壁部を有する。側壁部は、底部に対して垂直に形成される。外装体１の寸法は特に限定されないが、一例としては、横方向長さが６０～１６０ｍｍ、高さが６０～１００ｍｍ、厚みが１０～４０ｍｍである。 The exterior body 1 has a bottom portion having a substantially rectangular shape when viewed from the bottom surface, and a side wall portion erected on the peripheral edge of the bottom portion. The side wall is formed perpendicular to the bottom. The dimensions of the exterior body 1 are not particularly limited, but as an example, the exterior body 1 has a lateral length of 60 to 160 mm, a height of 60 to 100 mm, and a thickness of 10 to 40 mm.
　正極は、金属製の正極芯体と、芯体の両面に形成された正極合材層とを有する長尺体であって、短手方向における一方の端部に長手方向に沿って正極芯体が露出する帯状の正極芯体露出部４が形成されたものである。同様に、負極は、金属製の負極芯体と、芯体の両面に形成された負極合材層とを有する長尺体であって、短手方向における一方の端部に長手方向に沿って負極芯体が露出する帯状の負極芯体露出部５が形成されたものである。電極体３は、軸方向一端側に正極の正極芯体露出部４が、軸方向他端側に負極の負極芯体露出部５がそれぞれ配置された状態で、セパレータを介して正極及び負極が巻回された構造を有する。 The positive electrode is a long body having a metal positive electrode core body and positive electrode mixture layers formed on both sides of the core body, and is a positive electrode core body along the longitudinal direction at one end in the lateral direction. The strip-shaped positive electrode core body exposed portion 4 is formed. Similarly, the negative electrode is a long body having a negative electrode core made of metal and a negative electrode mixture layer formed on both sides of the core, along the longitudinal direction at one end in the lateral direction. A band-shaped negative electrode core body exposed portion 5 is formed in which the negative electrode core body is exposed. In the electrode body 3, the positive electrode core body exposed portion 4 of the positive electrode is arranged on one end side in the axial direction, and the negative electrode core body exposed portion 5 of the negative electrode is arranged on the other end side in the axial direction. It has a wound structure.
　正極の正極芯体露出部４の積層部には正極集電体６が、負極の負極芯体露出部５の積層部には負極集電体８がそれぞれ接続される。好適な正極集電体６は、アルミニウム製又はアルミニウム合金製である。好適な負極集電体８は、銅又は銅合金製である。正極端子７は、封口板２の電池外部側に配置される正極外部導電部１３と、正極外部導電部１３に接続された正極ボルト部１４と、封口板２に設けられた貫通穴に挿入される正極挿入部１５とを有し、正極集電体６と電気的に接続されている。また、負極端子９は、封口板２の電池外部側に配置される負極外部導電部１６と、負極外部導電部１６に接続された負極ボルト部１７と、封口板２に設けられた貫通穴に挿入される負極挿入部１８とを有し、負極集電体８と電気的に接続されている。 The positive electrode current collector 6 is connected to the laminated portion of the positive electrode core body exposed portion 4 of the positive electrode, and the negative electrode current collector 8 is connected to the laminated portion of the negative electrode core body exposed portion 5 of the negative electrode. A suitable positive electrode current collector 6 is made of aluminum or an aluminum alloy. A suitable negative electrode current collector 8 is made of copper or a copper alloy. The positive electrode terminal 7 is inserted into a positive electrode external conductive portion 13 arranged on the outer side of the battery of the sealing plate 2, a positive electrode bolt portion 14 connected to the positive electrode external conductive portion 13, and a through hole provided in the sealing plate 2. It has a positive electrode insertion portion 15 and is electrically connected to the positive electrode current collector 6. Further, the negative electrode terminal 9 is provided in a negative electrode external conductive portion 16 arranged on the outer side of the battery of the sealing plate 2, a negative electrode bolt portion 17 connected to the negative electrode external conductive portion 16, and a through hole provided in the sealing plate 2. It has a negative electrode insertion portion 18 to be inserted, and is electrically connected to the negative electrode current collector 8.
　正極端子７及び正極集電体６は、それぞれ内部側絶縁部材及び外部側絶縁部材を介して封口板２に固定される。内部側絶縁部材は、封口板２と正極集電体６との間に配置され、外部側絶縁部材は封口板２と正極端子７との間に配置される。同様に、負極端子９及び負極集電体８は、それぞれ内部側絶縁部材及び外部側絶縁部材を介して封口板２に固定される。内部側絶縁部材は封口板２と負極集電体８との間に配置され、外部側絶縁部材は封口板２と負極端子９との間に配置される。 The positive electrode terminal 7 and the positive electrode current collector 6 are fixed to the sealing plate 2 via the inner side insulating member and the outer side insulating member, respectively. The internal insulating member is arranged between the sealing plate 2 and the positive electrode current collector 6, and the external insulating member is arranged between the sealing plate 2 and the positive electrode terminal 7. Similarly, the negative electrode terminal 9 and the negative electrode current collector 8 are fixed to the sealing plate 2 via the internal insulating member and the external insulating member, respectively. The internal insulating member is arranged between the sealing plate 2 and the negative electrode current collector 8, and the external insulating member is arranged between the sealing plate 2 and the negative electrode terminal 9.
　電極体３は、外装体１内に収容される。封口板２は、外装体１の開口縁部にレーザー溶接等により接続される。封口板２は電解質注液孔１０を有し、この電解質注液孔１０は外装体１内に電解質を注液した後、封止栓により電解質注液孔１０が封止される。封口板２には、電池内部の圧力が所定値以上となった場合にガスを排出するためのガス排出弁１１が形成されている。 The electrode body 3 is housed in the exterior body 1. The sealing plate 2 is connected to the opening edge of the exterior body 1 by laser welding or the like. The sealing plate 2 has an electrolyte injection hole 10, and the electrolyte injection hole 10 is sealed with a sealing plug after the electrolyte is injected into the exterior body 1. The sealing plate 2 is formed with a gas discharge valve 11 for discharging gas when the pressure inside the battery exceeds a predetermined value.
　以下、電極体３を構成する正極、負極、セパレータ、及び非水電解質について、特に正極を構成する正極合材層について詳説する。 Hereinafter, the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte constituting the electrode body 3 will be described in detail, and in particular, the positive electrode mixture layer constituting the positive electrode will be described in detail.
　［正極］
　正極は、正極芯体と、正極芯体の表面に形成された正極合材層とを備える。正極芯体には、アルミニウム、アルミニウム合金など、正極の電位範囲で安定な金属の箔、当該金属を表層に配置したフィルム等を用いることができる。 [Positive electrode]
The positive electrode includes a positive electrode core body and a positive electrode mixture layer formed on the surface of the positive electrode core body. For the positive electrode core, a foil of a metal stable in the potential range of the positive electrode such as aluminum or an aluminum alloy, a film in which the metal is arranged on the surface layer, or the like can be used.
　正極合材層は、少なくとも、正極活物質と、導電助材としてのカーボンナノチューブ（以下、ＣＮＴという場合がある）と、結着材としてのポリフッ化ビニリデン（以下、ＰＶｄＦという場合がある）とを含む。正極は、正極芯体上に正極活物質、導電助材、及び結着材等を含む正極合材スラリーを塗布し、塗膜を乾燥させた後、圧縮して正極合材層を正極芯体の両面に形成することにより作製できる。正極合材層の厚みは、例えば、正極芯体の片側で１０μｍ～１５０μｍである。 The positive electrode mixture layer contains at least a positive electrode active material, carbon nanotubes as a conductive auxiliary material (hereinafter, may be referred to as CNT), and polyvinylidene fluoride as a binder (hereinafter, may be referred to as PVdF). Including. For the positive electrode, a positive electrode mixture slurry containing a positive electrode active material, a conductive auxiliary material, a binder, etc. is applied onto the positive electrode core, the coating film is dried, and then compressed to form the positive electrode mixture layer into the positive electrode core. It can be produced by forming on both sides of. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm on one side of the positive electrode core body.
　正極合材層の空隙率は、２３体積％～５０体積％である。正極合材層の空隙率は、正極合材層の嵩密度と、正極合材層に含まれる正極活物質、導電助材、結着材等の各成分の真密度及び含有量とから、以下の式に従って算出される。正極合材層の圧縮率を調整することで、正極合材層の嵩密度を変化させることができるので、正極合材層の空隙率を変えることができる。 The porosity of the positive electrode mixture layer is 23% by volume to 50% by volume. The void ratio of the positive electrode mixture layer is as follows based on the bulk density of the positive electrode mixture layer and the true density and content of each component such as the positive electrode active material, the conductive auxiliary material, and the binder contained in the positive electrode mixture layer. It is calculated according to the formula of. By adjusting the compressibility of the positive electrode mixture layer, the bulk density of the positive electrode mixture layer can be changed, so that the porosity of the positive electrode mixture layer can be changed.
　　　正極合材層の空隙率＝１－（成分毎の（含有量／真密度）の総和×正極合材層の嵩密度）
　正極合材層に含まれる正極活物質としては、Ｃｏ、Ｍｎ、Ｎｉ等の遷移金属元素を含有するリチウム遷移金属酸化物が例示できる。リチウム遷移金属酸化物は、例えばＬｉｘＣｏＯ２、ＬｉｘＮｉＯ２、ＬｉｘＭｎＯ２、ＬｉｘＣｏｙＮｉ１－ｙＯ２、ＬｉｘＣｏｙＭ１－ｙＯｚ、ＬｉｘＮｉ１－ｙＭｙＯｚ、ＬｉｘＭｎ２Ｏ４、ＬｉｘＭｎ２－ｙＭｙＯ４、ＬｉＭＰＯ４、Ｌｉ２ＭＰＯ４Ｆ（Ｍ；Ｎａ、Ｍｇ、Ｓｃ、Ｙ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ａｌ、Ｃｒ、Ｐｂ、Ｓｂ、Ｂのうち少なくとも１種、０＜ｘ≦１．２、０＜ｙ≦０．９、２．０≦ｚ≦２．３）である。これらは、１種単独で用いてもよいし、複数種を混合して用いてもよい。非水電解質二次電池の高容量化を図ることができる点で、正極活物質は、ＬｉｘＮｉＯ２、ＬｉｘＣｏｙＮｉ１－ｙＯ２、ＬｉｘＮｉ１－ｙＭｙＯｚ（Ｍ；Ｎａ、Ｍｇ、Ｓｃ、Ｙ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ａｌ、Ｃｒ、Ｐｂ、Ｓｂ、Ｂのうち少なくとも１種、０＜ｘ≦１．２、０＜ｙ≦０．９、２．０≦ｚ≦２．３）等のリチウムニッケル複合酸化物を含むことが好ましい。 Porosity of the positive electrode mixture layer = 1- (total of (content / true density) for each component x bulk density of the positive electrode mixture layer)
Examples of the positive electrode active material contained in the positive electrode mixture layer include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Lithium transition metal oxides, for example, Li x CoO 2, Li x NiO 2, Li x MnO 2, Li x Co y Ni 1-y O 2, Li x Co y M 1-y O z, Li x Ni 1- y M y O z, Li x Mn 2 O 4, Li x Mn 2-y M y O 4, LiMPO 4, Li 2 MPO 4 F (M; Na, Mg, Sc, Y, Mn, Fe, Co, Ni , Cu, Zn, Al, Cr, Pb, Sb, B, 0 <x ≦ 1.2, 0 <y ≦ 0.9, 2.0 ≦ z ≦ 2.3). These may be used alone or in admixture of a plurality of types. In that it can increase the capacity of the nonaqueous electrolyte secondary battery, the positive electrode active material, Li x NiO 2, Li x Co y Ni 1-y O 2, Li x Ni 1-y M y O z ( M; At least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0 <x≤1.2, 0 <y≤0. It is preferable to contain a lithium nickel composite oxide such as 9.9, 2.0 ≦ z ≦ 2.3).
　正極合材層に含まれるＣＮＴは、単層カーボンナノチューブ（ＳＷＣＮＴ）、多層カーボンナノチューブ（ＭＷＣＮＴ）のいずれであってもよい。また、ＭＷＣＮＴとしては、例えば、炭素六員環からなるグラフェンシートが繊維軸に対して平行に巻いたチューブラー構造のＣＮＴ、炭素六員環からなるグラフェンシートが繊維軸に対して垂直に配列したプーレトレット構造のＣＮＴ、炭素六員環からなるグラフェンシートが繊維軸に対して斜めの角度を持って巻いているヘリンボーン構造のＣＮＴ等を用いることができる。正極合材層は、ＣＮＴ以外に、導電助材として、カーボンブラック、アセチレンブラック（ＡＢ）、ケッチェンブラック、黒鉛等の炭素材料を含んでもよい。 The CNT contained in the positive electrode mixture layer may be either a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT). As MWCNTs, for example, a CNT having a tubular structure in which a graphene sheet made of a 6-membered carbon ring is wound parallel to the fiber axis, and a graphene sheet made of a 6-membered carbon ring are arranged perpendicular to the fiber axis. A CNT having a puretlet structure, a CNT having a herringbone structure in which a graphene sheet composed of a six-membered carbon ring is wound at an oblique angle with respect to the fiber axis, or the like can be used. In addition to CNT, the positive electrode mixture layer may contain a carbon material such as carbon black, acetylene black (AB), Ketjen black, and graphite as a conductive auxiliary material.
　ＣＮＴは、粒子径が５ｎｍ～４０ｎｍで、アスペクト比が１００～１０００である。この範囲を満たすことで、ＰＶｄＦとの相互作用が生じて、正極及び電池を低抵抗にすることができる。ここで、ＣＮＴの粒子径は、走査型電子顕微鏡（以下、ＳＥＭという場合がある）を用いて１０本のＣＮＴの直径を測定し、それらの平均値から算出される。また、ＣＮＴの長さは、ＳＥＭを用いて１０本のＣＮＴの長さを測定し、それらの平均値から算出される。例えば、ＣＮＴは、ＳＥＭを用いて加速電圧５ｋＶにて観察し、５万倍の画像（画素数１０２４×１２８０）において、任意の１０本のＣＮＴの直径及び長さを測定し、それらの平均値から粒子径及び長さを求めることができる。アスペクト比は、長さを粒子径で除した値である。 CNT has a particle size of 5 nm to 40 nm and an aspect ratio of 100 to 1000. By satisfying this range, interaction with PVdF occurs, and the positive electrode and the battery can have low resistance. Here, the particle size of CNTs is calculated from the average value of 10 CNTs measured by measuring the diameters of 10 CNTs using a scanning electron microscope (hereinafter, may be referred to as SEM). The length of CNTs is calculated by measuring the lengths of 10 CNTs using SEM and averaging them. For example, the CNT is observed at an acceleration voltage of 5 kV using SEM, and the diameter and length of any 10 CNTs are measured in an image (number of pixels 1024 x 1280) of 50,000 times, and the average value thereof is measured. The particle size and length can be obtained from. The aspect ratio is a value obtained by dividing the length by the particle size.
　正極合材層におけるＣＮＴの含有量は、０．２質量％～５質量％であり、好ましくは、１．５質量％～３質量％である。この範囲にあることで、正極合材スラリー中でのＣＮＴの分散性が向上するので、より低抵抗の正極及び電池が得られる。 The content of CNT in the positive electrode mixture layer is 0.2% by mass to 5% by mass, preferably 1.5% by mass to 3% by mass. Within this range, the dispersibility of CNTs in the positive electrode mixture slurry is improved, so that a positive electrode and a battery having lower resistance can be obtained.
　正極合材層の単位質量当たりに含まれるＰＶｄＦの分子数量は、０．００５～０．０３０であり、好ましくは０．００７～０．０１１である。この範囲を満たすことで、ＣＮＴとの相互作用が生じて、正極及び電池を低抵抗にすることができる。ここで、正極合材層の単位質量当たりに含まれるＰＶｄＦの分子数量とは、正極合材層におけるＰＶｄＦの含有量（質量％）をＰＶｄＦの分子量（ｇ／モル）で除した値である。 The molecular quantity of PVdF contained in the unit mass of the positive electrode mixture layer is 0.005 to 0.030, preferably 0.007 to 0.011. By satisfying this range, interaction with CNT occurs, and the positive electrode and the battery can have low resistance. Here, the molecular quantity of PVdF contained in the unit mass of the positive electrode mixture layer is a value obtained by dividing the content (mass%) of PVdF in the positive electrode mixture layer by the molecular weight (g / mol) of PVdF.
　正極合材層におけるポリフッ化ビニリデンの含有量が、０．３質量％～２．５質量％であってもよい。これにより、より低抵抗の正極及び電池が得られる。 The content of polyvinylidene fluoride in the positive electrode mixture layer may be 0.3% by mass to 2.5% by mass. As a result, a positive electrode and a battery having a lower resistance can be obtained.
　ポリフッ化ビニリデンの分子量は、１１０万～１４０万であってもよい。これにより、より低抵抗の正極及び電池が得られる。また、正極合材層は、ＰＶｄＦ以外に、結着材として、ポリテトラフルオロエチレン（ＰＴＦＥ）等のフッ素樹脂、ポリアクリロニトリル（ＰＡＮ）、ポリイミド、アクリル樹脂、ポリオレフィン等を含んでもよく、これらの樹脂と、カルボキシメチルセルロース（ＣＭＣ）又はその塩、ポリエチレンオキシド（ＰＥＯ）などが併用されてもよい。 The molecular weight of polyvinylidene fluoride may be 1.1 million to 1.4 million. As a result, a positive electrode and a battery having a lower resistance can be obtained. In addition to PVdF, the positive electrode mixture layer may contain a fluororesin such as polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, etc. as a binder, and these resins may be contained. And carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO) and the like may be used in combination.
　［負極］
　負極は、負極芯体と、負極芯体の表面に形成された負極合材層とを有する。負極芯体には、銅、銅合金等の負極の電位範囲で安定な金属の箔、当該金属を表層に配置したフィルムなどを用いることができる。負極合材層は、負極活物質、及び結着材を含む。負極合材層の厚みは、例えば集電体の片側で１０μｍ～１５０μｍである。負極は、負極芯体上に負極活物質、結着材等を含む負極合材スラリーを塗布し、塗膜を乾燥させた後、圧延して負極合材層を負極芯体の両面に形成することにより作製できる。 [Negative electrode]
The negative electrode has a negative electrode core body and a negative electrode mixture layer formed on the surface of the negative electrode core body. As the negative electrode core, a metal foil stable in the potential range of the negative electrode such as copper or a copper alloy, a film in which the metal is arranged on the surface layer, or the like can be used. The negative electrode mixture layer contains a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm to 150 μm on one side of the current collector. For the negative electrode, a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. is applied onto the negative electrode core body, the coating film is dried, and then rolled to form negative electrode mixture layers on both sides of the negative electrode core body. Can be produced by.
　負極活物質としては、リチウムイオンを可逆的に吸蔵、放出できるものであれば特に限定されず、一般的には黒鉛等の炭素材料が用いられる。黒鉛は、鱗片状黒鉛、塊状黒鉛、土状黒鉛等の天然黒鉛、塊状人造黒鉛、黒鉛化メソフェーズカーボンマイクロビーズ等の人造黒鉛のいずれであってもよい。また、負極活物質として、Ｓｉ、Ｓｎ等のＬｉと合金化する金属、Ｓｉ、Ｓｎ等を含む金属化合物、リチウムチタン複合酸化物などを用いてもよい。例えば、ＳｉＯｘ（０．５≦ｘ≦１．６）で表されるＳｉ含有化合物、又はＬｉ２ｙＳｉＯ（２＋ｙ）（０＜ｙ＜２）で表されるリチウムシリケート相中にＳｉの微粒子が分散したＳｉ含有化合物などが、黒鉛と併用されてもよい。 The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium ions, and a carbon material such as graphite is generally used. The graphite may be any of natural graphite such as scaly graphite, massive graphite and earthy graphite, and artificial graphite such as massive artificial graphite and graphitized mesophase carbon microbeads. Further, as the negative electrode active material, a metal alloying with Li such as Si and Sn, a metal compound containing Si and Sn and the like, a lithium titanium composite oxide and the like may be used. For example, Si-containing compounds represented by SiO x (0.5 ≦ x ≦ 1.6) or lithium silicate phases represented by Li 2y SiO (2 + y) (0 <y <2) contain fine particles of Si. Dispersed Si-containing compounds and the like may be used in combination with graphite.
　負極合材層に含まれる結着材には、正極の場合と同様に、ＰＴＦＥ、ＰＶｄＦ等の含フッ素樹脂、ＰＡＮ、ポリイミド、アクリル樹脂、ポリオレフィンなどを用いてもよいが、好ましくはスチレン－ブタジエンゴム（ＳＢＲ）が用いられる。また、負極合材層には、ＣＭＣ又はその塩、ポリアクリル酸（ＰＡＡ）又はその塩、ポリビニルアルコール（ＰＶＡ）などが含まれていてもよい。負極合材層には、例えばＳＢＲと、ＣＭＣ又はその塩が含まれる。 As the binder contained in the negative electrode mixture layer, a fluororesin such as PTFE or PVdF, PAN, polyimide, acrylic resin, polyolefin or the like may be used as in the case of the positive electrode, but styrene-butadiene is preferable. Rubber (SBR) is used. Further, the negative electrode mixture layer may contain CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA) and the like. The negative electrode mixture layer contains, for example, SBR and CMC or a salt thereof.
　［セパレータ］
　セパレータには、イオン透過性及び絶縁性を有する多孔性シートが用いられる。多孔性シートの具体例としては、微多孔薄膜、織布、不織布等が挙げられる。セパレータの材質としては、ポリエチレン、ポリプロピレン等のポリオレフィン、セルロースなどが好適である。セパレータは、単層構造であってもよく、積層構造を有していてもよい。また、セパレータの表面には、アラミド樹脂等の耐熱性の高い樹脂層、無機化合物のフィラーを含むフィラー層が設けられていてもよい。 [Separator]
As the separator, a porous sheet having ion permeability and insulating property is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a non-woven fabric. As the material of the separator, polyolefins such as polyethylene and polypropylene, cellulose and the like are suitable. The separator may have a single-layer structure or a laminated structure. Further, the surface of the separator may be provided with a resin layer having high heat resistance such as an aramid resin and a filler layer containing a filler of an inorganic compound.
　［非水電解質］
　非水電解質は、非水溶媒と、非水溶媒に溶解した電解質塩とを含む。非水溶媒には、例えばエステル類、エーテル類、アセトニトリル等のニトリル類、ジメチルホルムアミド等のアミド類、及びこれらの２種以上の混合溶媒等を用いることができる。非水溶媒は、これら溶媒の水素の少なくとも一部をフッ素等のハロゲン原子で置換したハロゲン置換体を含有していてもよい。ハロゲン置換体としては、フルオロエチレンカーボネート（ＦＥＣ）等のフッ素化環状炭酸エステル、フッ素化鎖状炭酸エステル、フルオロプロピオン酸メチル（ＦＭＰ）等のフッ素化鎖状カルボン酸エステルなどが挙げられる。 [Non-aqueous electrolyte]
The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these can be used. The non-aqueous solvent may contain a halogen substituent in which at least a part of hydrogen in these solvents is substituted with a halogen atom such as fluorine. Examples of the halogen substituent include a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC), a fluorinated chain carbonate, and a fluorinated chain carboxylic acid ester such as methyl fluoropropionate (FMP).
　上記エステル類の例としては、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート等の環状炭酸エステル、ジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）、ジエチルカーボネート（ＤＥＣ）、メチルプロピルカーボネート、エチルプロピルカーボネート、メチルイソプロピルカーボネート等の鎖状炭酸エステル、γ－ブチロラクトン（ＧＢＬ）、γ－バレロラクトン（ＧＶＬ）等の環状カルボン酸エステル、酢酸メチル、酢酸エチル、酢酸プロピル、プロピオン酸メチル（ＭＰ）、プロピオン酸エチル等の鎖状カルボン酸エステルなどが挙げられる。 Examples of the above esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and methylpropyl carbonate. , Ethylpropyl carbonate, chain carbonate such as methyl isopropyl carbonate, cyclic carboxylic acid ester such as γ-butyrolactone (GBL), γ-valerolactone (GVL), methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP) ), Chain carboxylic acid ester such as ethyl propionate and the like.
　上記エーテル類の例としては、１，３－ジオキソラン、４－メチル－１，３－ジオキソラン、テトラヒドロフラン、２－メチルテトラヒドロフラン、プロピレンオキシド、１，２－ブチレンオキシド、１，３－ジオキサン、１，４－ジオキサン、１，３，５－トリオキサン、フラン、２－メチルフラン、１，８－シネオール、クラウンエーテル等の環状エーテル、１，２－ジメトキシエタン、ジエチルエーテル、ジプロピルエーテル、ジイソプロピルエーテル、ジブチルエーテル、ジヘキシルエーテル、エチルビニルエーテル、ブチルビニルエーテル、メチルフェニルエーテル、エチルフェニルエーテル、ブチルフェニルエーテル、ペンチルフェニルエーテル、メトキシトルエン、ベンジルエチルエーテル、ジフェニルエーテル、ジベンジルエーテル、o－ジメトキシベンゼン、１，２－ジエトキシエタン、１，２－ジブトキシエタン、ジエチレングリコールジメチルエーテル、ジエチレングリコールジエチルエーテル、ジエチレングリコールジブチルエーテル、１，１－ジメトキシメタン、１，１－ジエトキシエタン、トリエチレングリコールジメチルエーテル、テトラエチレングリコールジメチルエーテル等の鎖状エーテルなどが挙げられる。 Examples of the above ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahexyl, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4. -Cyclic ethers such as dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether , Dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxy toluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxy Chain ethers such as ethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc. And so on.
　電解質塩は、リチウム塩であることが好ましい。リチウム塩の例としては、ＬｉＢＦ４、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＡｌＣｌ４、ＬｉＳＣＮ、ＬｉＣＦ３ＳＯ３、ＬｉＣＦ３ＣＯ２、Ｌｉ（Ｐ（Ｃ２Ｏ４）Ｆ４）、ＬｉＰＦ６－ｘ（ＣｎＦ２ｎ＋１）ｘ（１＜ｘ＜６，ｎは１又は２）、ＬｉＢ１０Ｃｌ１０、ＬｉＣｌ、ＬｉＢｒ、ＬｉＩ、クロロボランリチウム、低級脂肪族カルボン酸リチウム、Ｌｉ２Ｂ４Ｏ７、Ｌｉ（Ｂ（Ｃ２Ｏ４）Ｆ２）等のホウ酸塩類、ＬｉＮ（ＳＯ２ＣＦ３）２、ＬｉＮ（Ｃ１Ｆ２ｌ＋１ＳＯ２）（ＣｍＦ２ｍ＋１ＳＯ２）｛ｌ，ｍは０以上の整数｝等のイミド塩類などが挙げられる。リチウム塩は、これらを１種単独で用いてもよいし、複数種を混合して用いてもよい。これらのうち、イオン伝導性、電気化学的安定性等の観点から、ＬｉＰＦ６を用いることが好ましい。リチウム塩の濃度は、例えば非水溶媒１Ｌ当り０．８モル～１．８モルである。 The electrolyte salt is preferably a lithium salt. Examples of the lithium salt, LiBF 4, LiClO 4, LiPF 6, LiAsF 6, LiSbF 6, LiAlCl 4, LiSCN, LiCF 3 SO 3, LiCF 3 CO 2, Li (P (C 2 O 4) F 4), LiPF 6-x (C n F 2n + 1 ) x (1 <x <6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, Li 2 B 4 O 7 , borates such as Li (B (C 2 O 4 ) F 2 ), LiN (SO 2 CF 3 ) 2 , LiN (C 1 F 2l + 1 SO 2 ) (C m F 2m + 1 SO 2 ) {l , M is an integer of 0 or more} and other imide salts. As the lithium salt, these may be used individually by 1 type, or a plurality of types may be mixed and used. Of these, LiPF 6 is preferably used from the viewpoint of ionic conductivity, electrochemical stability, and the like. The concentration of the lithium salt is, for example, 0.8 mol to 1.8 mol per 1 L of the non-aqueous solvent.
　＜実施例＞
　以下、実施例により本開示をさらに説明するが、本開示はこれらの実施例に限定されるものではない。 <Example>
Hereinafter, the present disclosure will be further described with reference to Examples, but the present disclosure is not limited to these Examples.
　＜実施例１＞
　［正極の作製］
　正極活物質として、ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２で表されるリチウム遷移金属酸化物を用いた。導電助材としてのＣＮＴは、粒子径が１０ｎｍで、アスペクト比が１００～１０００のもの（以下、ＣＮＴ－Ａ）を用いた。ＰＶｄＦは、分子量が１１０万のものを用いた。正極活物質と、ＣＮＴと、ＰＶｄＦとを、９７．３：０．２：２．５の質量比で混合し、Ｎ－メチル－２－ピロリドン（ＮＭＰ）を加えながら混錬して、正極合材スラリーを調製した。次に、アルミニウム箔からなる正極芯体リードが接続される部分を残して、当該正極合材スラリーを両面に塗布し、塗膜を乾燥させた。そして、正極合材層の空隙率が５０体積％となるようにローラを用いて塗膜を圧延した後、所定の電極サイズに切断し、正極芯体の両面に正極合材層が形成された正極を作製した。 <Example 1>
[Preparation of positive electrode]
As the positive electrode active material, a lithium transition metal oxide represented by LiNi 1/3 Co 1/3 Mn 1/3 O 2 was used. As the CNT as the conductive auxiliary material, one having a particle size of 10 nm and an aspect ratio of 100 to 1000 (hereinafter referred to as CNT-A) was used. As PVdF, one having a molecular weight of 1.1 million was used. The positive electrode active material, CNT, and PVdF are mixed at a mass ratio of 97.3: 0.2: 2.5 and kneaded while adding N-methyl-2-pyrrolidone (NMP) to combine the positive electrodes. A material slurry was prepared. Next, the positive electrode mixture slurry was applied to both sides, leaving a portion to which the positive electrode core lead made of aluminum foil was connected, and the coating film was dried. Then, the coating film was rolled using a roller so that the porosity of the positive electrode mixture layer was 50% by volume, and then cut into a predetermined electrode size to form positive electrode mixture layers on both sides of the positive electrode core. A positive electrode was prepared.
　［負極の作製］
　負極活物質としての黒鉛と、ＣＭＣのナトリウム塩と、ＳＢＲのディスパージョンとを、９９／０．６／０．４の固形分質量比で混合し、水を適量加えて、負極合材スラリーを調製した。次に、銅箔からなる負極芯体の両面にリードが接続される部分を残して、負極合材スラリーを塗布し、塗膜を乾燥させた。そして、ローラを用いて塗膜を圧延した後、所定の電極サイズに切断し、負極芯体の両面に負極合材層が形成された負極を作製した。負極合材層の充填密度は１．１７ｇ／ｃｍ３であった。 [Preparation of negative electrode]
Graphite as a negative electrode active material, sodium salt of CMC, and dispersion of SBR are mixed at a solid content mass ratio of 99 / 0.6 / 0.4, and an appropriate amount of water is added to prepare a negative electrode mixture slurry. Prepared. Next, the negative electrode mixture slurry was applied and the coating film was dried, leaving the portions where the leads were connected to both sides of the negative electrode core made of copper foil. Then, after rolling the coating film using a roller, the coating film was cut to a predetermined electrode size to prepare a negative electrode having negative electrode mixture layers formed on both sides of the negative electrode core. The packing density of the negative electrode mixture layer was 1.17 g / cm 3 .
　［非水電解質の調製］
　エチレンカーボネート（ＥＣ）と、ジメチルカーボネート（ＤＭＣ）と、エチルメチルカーボネート（ＥＭＣ）とを、２５：３５：４０の体積比で混合した１００質量部の混合溶媒にビニレンカーボネート（ＶＣ）を１質量部添加し、ＬｉＰＦ６を１．１５モル／Ｌの割合で溶解させて非水電解質を調製した。 [Preparation of non-aqueous electrolyte]
1 part by mass of vinylene carbonate (VC) is added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC) are mixed at a volume ratio of 25:35:40. It was added and LiPF 6 was dissolved at a ratio of 1.15 mol / L to prepare a non-aqueous electrolyte.
　［試験セルの作製］
　上記負極及び上記正極にリードをそれぞれ取り付け、セパレータを介して各電極を１枚ずつ交互に積層された積層型の電極体を作製した。セパレータには、単層のポリプロピレン製セパレータを用いた。作製した電極体及び上記非水電解質を角形の電池ケースに収容して、試験セルを作製した。 [Preparation of test cell]
Leads were attached to the negative electrode and the positive electrode, respectively, and a laminated electrode body was prepared in which each electrode was alternately laminated one by one via a separator. A single-layer polypropylene separator was used as the separator. The prepared electrode body and the non-aqueous electrolyte were housed in a square battery case to prepare a test cell.
　［合材層抵抗及び界面抵抗の測定］
　試験セルに組み込む前の正極において、合材層全体の抵抗である合材層抵抗（Ω・ｃｍ）、及び、正極芯体と正極合材層との間の抵抗である界面抵抗（Ω・ｃｍ２）を測定した。合材層抵抗増加量及び界面抵抗増加量は、上記のように作製した正極についての測定結果を、正極を８０℃のジメチルカーボネート（ＤＭＣ）に１８時間浸漬した後に取り出した正極についての測定結果から引くことで算出した。合材層抵抗及び界面抵抗の測定には、日置電機株式会社製の電極抵抗測定器（装置名：ＸＦ０５７）を用いた。 [Measurement of mixture layer resistance and interfacial resistance]
In the positive electrode before being incorporated into the test cell, the mixture layer resistance (Ω · cm), which is the resistance of the entire mixture layer, and the interfacial resistance (Ω · cm), which is the resistance between the positive electrode core and the positive electrode mixture layer. 2 ) was measured. The amount of increase in mixture layer resistance and the amount of increase in interfacial resistance are determined from the measurement results for the positive electrode prepared as described above, and the measurement results for the positive electrode taken out after immersing the positive electrode in dimethyl carbonate (DMC) at 80 ° C. for 18 hours. Calculated by subtracting. An electrode resistance measuring instrument (device name: XF057) manufactured by Hioki Electric Co., Ltd. was used for measuring the mixture layer resistance and the interfacial resistance.
　［直流抵抗の評価］
　上記試験セルに対して、２５℃の環境下で、０．３Ｃの定電流で充電深度（ＳＯＣ）が５０％になるまで定電流充電を行い、ＳＯＣ５０％到達後、電流値が０．０２Ｃになるまで定電圧充電を行った。その後、５０Ｃの定電流で１０秒間の定電流放電を行った。直流抵抗は、以下の式のように、開回路電圧（ＯＣＶ）と、放電から１０秒後の閉回路電圧（ＣＣＶ）との差を、放電から１０秒後の放電電流で除すことで算出した。 [Evaluation of DC resistance]
The above test cell is constantly charged with a constant current of 0.3 C until the charging depth (SOC) reaches 50% in an environment of 25 ° C., and after reaching 50% SOC, the current value reaches 0.02 C. Constant voltage charging was performed until it became. Then, a constant current discharge of 50 C was performed for 10 seconds. The DC resistance is calculated by dividing the difference between the open circuit voltage (OCV) and the closed circuit voltage (CCV) 10 seconds after discharge by the discharge current 10 seconds after discharge, as shown in the following equation. did.
　　　直流抵抗＝［ＯＣＶ－ＣＣＶ（放電１０秒後）］／放電電流（放電１０秒後）
　＜実施例２～１４、比較例１～２１＞
　表１、表２に示すように、正極活物質の含有量、導電助剤の種類及び含有量、ＰＶｄＦの含有量及び分子量、並びに正極合材層の空隙率を変更したこと以外は、実施例１と同様にして正極及び試験セルを作製して評価を行った。なお、導電助材のＣＮＴ－Ｂは、粒子径が１５０ｎｍで、アスペクト比が１０～７０のＣＮＴである。 DC resistance = [OCV-CCV (10 seconds after discharge)] / Discharge current (10 seconds after discharge)
<Examples 2 to 14, Comparative Examples 1 to 21>
Examples are shown in Tables 1 and 2, except that the content of the positive electrode active material, the type and content of the conductive auxiliary agent, the content and molecular weight of PVdF, and the porosity of the positive electrode mixture layer are changed. A positive electrode and a test cell were prepared and evaluated in the same manner as in 1. The conductive auxiliary material CNT-B is a CNT having a particle size of 150 nm and an aspect ratio of 10 to 70.
　表１と表２に、実施例及び比較例の、合材層抵抗増加量、界面抵抗増加量、直流抵抗の結果をまとめた。また、表１、表２には、正極活物質、導電助材、ＰＶｄＦからなる正極合材層の組成、及び正極合材層の空隙率も記載した。 Tables 1 and 2 summarize the results of the mixture layer resistance increase, the interface resistance increase, and the DC resistance of Examples and Comparative Examples. In addition, Tables 1 and 2 also show the composition of the positive electrode mixture layer composed of the positive electrode active material, the conductive auxiliary material, and PVdF, and the porosity of the positive electrode mixture layer.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　表１、表２から分かるように、実施例１～１４はいずれも、比較例１～２１と比較して、正極及び電池の抵抗が小さかった。また、実施例１～１４で、正極合材層における正極活物質の含有量は９０質量％以上であり、高容量な正極及び電池を作製できた。 As can be seen from Tables 1 and 2, in each of Examples 1 to 14, the resistance of the positive electrode and the battery was smaller than that of Comparative Examples 1 to 21. Further, in Examples 1 to 14, the content of the positive electrode active material in the positive electrode mixture layer was 90% by mass or more, and a high-capacity positive electrode and a battery could be produced.
１　　外装体
２　　封口板
３　　電極体
４　　正極芯体露出部
５　　負極芯体露出部
６　　正極集電体
７　　正極端子
８　　負極集電体
９　　負極端子
１０　　電解質注液孔
１１　　ガス排出弁
１３　　正極外部導電部
１４　　正極ボルト部
１５　　正極挿入部
１６　　負極外部導電部
１７　　負極ボルト部
１８　　負極挿入部
１００　　二次電池 1 Exterior body 2 Seal plate 3 Electrode body 4 Positive electrode core body Exposed part 5 Negative electrode core body exposed part 6 Positive current collector 7 Positive electrode terminal 8 Negative electrode current collector 9 Negative electrode terminal 10 Electrode injection hole 11 Gas discharge valve 13 Positive electrode External conductivity Part 14 Positive electrode bolt part 15 Positive electrode insertion part 16 Negative electrode external conductive part 17 Negative electrode bolt part 18 Negative electrode insertion part 100 Secondary battery

Claims (4)

  1. 　正極芯体と、前記正極芯体の表面に形成された正極合材層と、を備え、
    　前記正極合材層の空隙率は、２３体積％～５０体積％であり、
    　前記正極合材層は、少なくとも、正極活物質と、導電助材としてのカーボンナノチューブと、結着材としてのポリフッ化ビニリデンを含み、
    　カーボンナノチューブは、粒子径が５ｎｍ～４０ｎｍで、アスペクト比が１００～１０００で、前記正極合材層における含有量が０．２質量％～５質量％であり、
    　前記正極合材層の単位質量当たりに含まれるポリフッ化ビニリデンの分子数量が０．００５～０．０３０である、非水電解質二次電池用正極。     A positive electrode core body and a positive electrode mixture layer formed on the surface of the positive electrode core body are provided.
    The porosity of the positive electrode mixture layer is 23% by volume to 50% by volume.
    The positive electrode mixture layer contains at least a positive electrode active material, carbon nanotubes as a conductive auxiliary material, and polyvinylidene fluoride as a binder.
    The carbon nanotubes have a particle size of 5 nm to 40 nm, an aspect ratio of 100 to 1000, and a content in the positive electrode mixture layer of 0.2% by mass to 5% by mass.
    A positive electrode for a non-aqueous electrolyte secondary battery in which the molecular quantity of polyvinylidene fluoride contained in the unit mass of the positive electrode mixture layer is 0.005 to 0.030.
  2. 　前記正極合材層におけるポリフッ化ビニリデンの含有量が、０．３質量％～２．５質量％である、請求項１に記載の非水電解質二次電池用正極。 The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of polyvinylidene fluoride in the positive electrode mixture layer is 0.3% by mass to 2.5% by mass.
  3. 　ポリフッ化ビニリデンの分子量は、１１０万～１４０万である、請求項１又は２に記載の非水電解質二次電池用正極。 The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the polyvinylidene fluoride has a molecular weight of 1.1 million to 1.4 million.
  4. 　請求項１～３のいずれか１項に記載の非水電解質二次電池用正極と、負極と、非水電解質とを備える、非水電解質二次電池。 A non-aqueous electrolyte secondary battery comprising the positive electrode, the negative electrode, and the non-aqueous electrolyte for the non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.
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